Neonicotinoid pesticides cause mass fatalities of native bumble bees: A case study from Wilsonville, Oregon, USA

Authors: HATFIELD, RICHARD - The Xerces Society; STRANGE, JAMES - The Ohio State University; Koch, Jonathan; JEPSEN, SARIAN - The Xerces Society; STAPLETON, ISAAK - Oregon Department Of Agriculture

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/27/2021
Publication Date: 6/19/2021
Citation: Hatfield, R., Strange, J.P., Koch, J., Jepsen, S., Stapleton, I. 2021. Neonicotinoid pesticides cause mass fatalities of native bumble bees: A case study from Wilsonville, Oregon, USA. Environmental Entomology. https://doi.org/10.1093/ee/nvab059.
DOI: https://doi.org/10.1093/ee/nvab059

Interpretive Summary: In June of 2013 an application of dinotefuran on an ornamental planting of European linden trees (Tilia cordata) in a suburban shopping mall parking lot in Wilsonville, Oregon provoked the largest documented pesticide kill of bumble bees in North America. In this study, we use ground surveys and microsatellite markers to estimate the number of Vosnesensky bumble bees (Bombus vosnesenskii) that were killed and provide evidence that the cause of death was dinotefuran contaminated T. cordata flowers. We present information on the dinotefuran application rates that were applied to the T. cordata and the residue levels of neonicotinoids on sampled T. cordata flowers and tissues of dead B. vosnesenskii. Given the negative impact of the legal dinotefuran application on pollinating insects in a commercial setting, we discuss best pesticide and landscape management practices.

Technical Abstract: In June of 2013 an application of dinotefuran on an ornamental planting of European linden trees (Tilia cordata) in a shopping mall parking lot in Wilsonville, Oregon provoked the largest documented pesticide kill of bumble bees in North America. Based on geographic information systems and population genetic analysis, we estimate that at least 54,519 bumble bees representing between 289 and 596 colonies were killed during this event. Dinotefuran is a neonicotinoid that is highly effective in exterminating and/or harming target pest insects and non-target beneficial insects. Pesticide analysis of flowers that received foliar application revealed that the concentration of dinotefuran exceeded the LC50 of the beneficial pollinator, the European honey bee (Apis mellifera) from 800 % - 3,767%. In fact, the minimum reported dinotefuran concentration of a sampled T. cordata flower was 7.4 ppm, or in excess of 737% above the LC50 of A. mellifera. Furthermore, sampled bumble bees of the species Bombus vosnesenskii were found to have a dinotefuran concentration of 0.92 ppm at the time of death, which also exceeds the maximum LC50 of A. mellifera (=0.884 ppm). Our study underscores the lethal impact of the neonicotinoid pesticide dinotefuran on pollinating insect populations in a suburban environment. To our knowledge, the documentation and impact of pesticide kills on wild populations of beneficial insects has not been reported in the scientific literature. It is likely that the vast majority of mass pesticide kills of beneficial insects across other environments go unreported and unnoticed.